There is high commercial demand for additively manufactured (3D-printed) ceramics in fields including industrial filtration (molten metal filters, flow separators); metal processing (casting molds/blanks); implantable dental and medical devices; and semiconductor processing. Additive manufacturing of ceramic materials is also of interest for propulsion components, thermal protection systems, porous burners, microelectromechanical systems, and electronic device packaging, for example.
In comparison with metals and polymers, ceramics are difficult to process, particularly into complex shapes. Because they cannot be cast or machined easily, ceramics are typically consolidated from powders by sintering or deposited in thin films. Flaws, such as porosity and inhomogeneity introduced during processing, govern the strength because the flaws initiate cracks, and brittle ceramics have little ability to resist fracture. This processing challenge has limited the ability to take advantage of ceramics' impressive properties, including high-temperature capability, environmental resistance, and high strength.
Ceramic matrix composite (CMC) materials overcome many disadvantages of conventional ceramics, such as brittle failure, low fracture toughness, and limited thermal shock resistance. Applications of ceramic matrix composites include those requiring reliability at high temperatures (beyond the capability of metals or polymers) and resistance to corrosion and wear.
No mature method for 3D printing ceramic matrix composites exists. Currently, CMC materials are limited to manual lay-up, molding, or thermoforming. There are also known techniques for sintering ceramic particles or using ceramic particles printed in a binder, both of which typically produce porous ceramics which have lower strength than the parent material. Ceramic structures are often sintered as compacted porous materials, severely limiting the manufacturable geometries.
Preceramic polymers are a class of polymers which allow, via a thermal treatment, a conversion of a polymer part to a ceramic material. Typically, these preceramic polymers contain silicon (Si) in the molecular backbone, with the resulting material containing Si. There are a wide variety of known preceramic polymers. Examples include polysilazanes, borazine-modified hydridopolysilazanes, polysilanes, polycarbosilanes, silicone resins, polyvinylborazine, polyborazylene, and decaborane-based polymers. These preceramic polymers have been used to form specific polymer-based structures that can be subsequently heat-treated (pyrolyzed or sintered) to create near net-shape ceramic structures.
Formulations have been described for creating ceramic materials, which can be printed (additively manufactured) with various methods such as stereolithography techniques and laser sintering. These are typically unreinforced ceramics and suffer from low fracture toughness. These methods are described in Zocca et al., “Additive Manufacturing of Ceramics: Issues, Potentialities, and Opportunities”, J. Am. Ceram. Soc., 98 [7] 1983-2001 (2015). In addition, formulations which can create 1D or 2D ceramics, or very small 3D structures, have been described. See U.S. Pat. No. 4,816,497 issued Mar. 28, 1989 to Lutz et al.; U.S. Pat. No. 5,698,485 issued Dec. 16, 1997 to Bruck et al.; U.S. Pat. No. 6,573,020 issued Jun. 3, 2003 to Hanemann et al.; U.S. Pat. No. 7,582,685 issued Sep. 1, 2009 to Arney et al.; and U.S. Patent App. Pub. No. US2006/0069176A1 published Mar. 30, 2006 to Bowman et al.
When a large, detailed ceramic object is desired, traditionally such ceramics have been machined from a fired or prefired (green) body to the final desired shape. Direct 3D printing of ceramics can reduce significantly the manufacturing costs of ceramic components. However, there are limitations on the sizes of parts that can be fabricated, based on 3D printing of preceramic polymers into a single part followed by pyrolysis of that part. Also, geometry errors can arise for complicated part geometries. Because of these challenges, parts of the preceramic type have typically been molded to shape rather than additively manufactured. Others have employed preceramic resins to join ceramic parts (i.e. parts which have already been pyrolyzed).
In view of the shortcomings in the art, methods and formulations to fabricate large ceramic objects with arbitrary geometries are still needed.